Acquisition of aerial imagery traces its history back to the Wright brothers, and is now commonly performed from satellite and space shuttle platforms, in addition to aircraft.
While the earliest aerial imagery relied on conventional film technology, a variety of electronic sensors are now more commonly used. Some collect image data corresponding to specific visible, UV or IR frequency spectra (e.g., the MultiSpectral Scanner and Thematic Mapper used by the Landsat satellites). Others use wide band sensors. Still others use radar or laser systems (sometimes stereo) to sense topological features in three dimensions. Other types of image collection rely on electro-optical panchromatic (grayscale), multi-spectral (less than 20 bands) and hyper-spectral (20 bands or more). Some satellites can even collect ribbon imagery (e.g., a raster-like, 1-demensional terrestrial representation, which is pieced together with other such adjacent ribbons).
The quality of the imagery has also constantly improved. Some satellite systems are now capable of acquiring image and topological data having a resolution of less than a meter. Aircraft imagery, collected from lower altitudes, provides still greater resolution.
A huge quantity of aerial imagery is constantly being collected. Management and coordination of the resulting large data sets is a growing problem. Integrating the imagery with related information is also a problem.
In accordance with one aspect of the present invention, digital watermarking technology is employed to help manage such imagery and related information, among other benefits. In another aspect, a digital watermark conveys information that is used to register or align geographic information system (GIS) layers with a corresponding image location, perhaps after the image has been distorted.
The foregoing and additional features and advantages of the present invention will be even more readily apparent from the following detailed description with reference to the following figures.